Older patients who present to the emergency department frequently have acute or chronic alterations of their mental status, including their level of consciousness and cognition. Recognizing both acute and chronic changes in cognition are important for emergency physicians. Delirium is an acute change in attention, awareness, and cognition. Numerous life-threatening conditions can cause delirium; therefore, prompt recognition and treatment are critical. The authors discuss an organized approach that can lead to a prompt diagnosis within the time constraints of the emergency department.